There are an after stretching system and a simultaneous opening system in an expanding work method. The after stretching system is one in which cut slits are first made in a sheet-shaped material and the cut slits are then expanded, as disclosed for example in Published Patent Application (KOKAI) No. 52-144745. The simultaneous opening system is one in which the cut slits are made in the sheet-shaped material and the cut slits are expanded simultaneously, and which is classified into a parallel cutter system and a right angle cutter system. The parallel cutter system is one which uses cutter lines comprising cutters arranged stepwise and in parallel each other so as to give broken lines parallel with a feed direction of the sheet-shaped material, as disclosed for example in Published Patent Application (KOKAI) No. 53-79760. The right angle cutter system is one in which one row of cutter lines arranged right angle to the feed direction of the sheet-shaped material is moved vertically and the cutters are swung in an arranged direction on every pitch in order to put meshes into zigzag positions, as disclosed for example in U.S. Pat. No. 3,310,438.
Generally, a grid for use in the lead acid storage battery plate has so far been manufactured by casting or machining. However, a percentage of manufacture by machining providing a high productivity is increasing in recent years, and a manufacturing method using expanding work of sheet-shaped material made of lead alloy is prevailing now as a typical machining work. A grid which is formed from an expanded sheet-shaped material made of copper alloy, attached by casting with a current collector plate having a lug, and coated with lead on its surface thereafter, may be mentioned as a grid for use in a comparatively large lead acid storage battery plate.
However, the above-mentioned after stretching system has included such a problem that a special expanding process has been required.
The parallel cutter system has included such a problem that a die-set having a very long cutter line has been required because a pitch of cutter has had to be made 1.5 times as large as a pitch in cut length direction of the sheet-shaped material and it had not been able to expand the cut lines largely in spite of an expanding direction being same with a direction of height of reticulated portion. The right angle cutter system has included such a problem that it has not been able to continuously manufacture the expanded mesh having a non-expanded part and a reticulated portion and a high-speed production has been impossible because it has been required to swing the cutter line.
The expanded mesh obtained by the conventional method has included a problem of poor current collecting efficiency because of an obtuse inclining angle of skeletal element composing the mesh relative to side edges.
In the above conventional system, only a cutter merely making the cut slits can be used as a cutter for forming a mesh adjacent to the non-expanded portion in order not to elongate the non-expanded portion. Therefore, the system has included such a problem that it has not been able to form a large mesh in this part and to effectively utilize the sheet-shaped material.
In the grid for use in a comparatively large lead acid storage battery plate, a current collector plate having a lug is formed separately and attached to the expanded mesh. In this way, a large expanded mesh is manufactured by the right angle cutter system. For this reason, there have been such problems that the expanded mesh has been corrugated over its entire circumference, a process for remedying the entire circumference after installing another members on it has been required and troublesome, and the remedy work has been hard.